This invention relates to aluminum powder metallurgy, and more particularly to methods of making sintered aluminum alloy particles having improved wear resistance from mixtures of aluminum and other metal powder or particles, as well as to the products of such methods.
In the production of an aluminum alloy article by powder metallurgical techniques as heretofore known, an aluminum premix powder (typically containing a major proportion of aluminum and a minor proportion of one or more alloying elements having high solubility with aluminum) is sintered, commonly after being compacted in the presence of a lubricant. In most instances, the premix is compacted in admixture with a lubricant, and sintering is effected in a dry non-oxidizing atmosphere, at a temperature which is above the solidus point of the alloy to ensure rupturing of oxide surface films on the metal particles as necessary for bonding. Alternatively, the premix may be very highly compacted (to at least 95% of theoretical density) without admixed lubricant, but with lubrication of the walls of the compacting die, and then sintered in air; the high degree of compaction, in such case, seals the surface of the compacted body before and during sintering, effectively providing a low dew point atmosphere within the body. A typical range of sintering temperatures, for present-day conventional aluminum premixes, is between about 590.degree. and 635.degree. C.
Among articles that may be produced in this way are bearings, face seals, thrust washers and others parts subject to wear and friction in use. While aluminum alloys offer various advantages, including light weight, stated in general it would be desirable to improve the wear resistance of such articles, e.g. at elevated temperatures.
There has been developed a class of intermetallic materials, which are cobalt or nickel-based alloys (containing molybdenum or tungsten as a principal alloying element together with silicon and, optionally, chromium) having a hard so-called Laves phase intermetallic present in a soft matrix, characterized by superior high-temperature wear resistance as well as by good corrosion resistance. Alloys of this general character are described, for example, in U.S. Pat. Nos. 3,180,012; 3,361,560; and 3,410,732. Specific compositions of this class are commercially available under the trade name "Tribaloy." It has been found that alloys of the described class, when incorporated in powdered or particulate form as an additive in a premix powder containing a major proportion of other metal powder such as iron, stainless steel, nickel or bronze, can impart properties of significantly improved wear resistance to articles produced by sintering the premix. Heretofore, however, it has not been possible to produce satisfactory sintered parts from aluminum premix powders containing such additive, because the inclusion of the additive resulted in weak, distorted, discolored articles.